Blocking wait for interrupt

[Sebastian Sumpf]

Hi Johannes,

On 07/27/2017 01:42 PM, Johannes Kliemann wrote:
> Hi Sebastian,
> 
> yes, that is the function I call from Genode.
> 
> And thanks in advance for helping me out.
> 

Good. I will try to explain how the Lx::Task approach is supposed to
work in this case:

Your task calls 'i2c_dw_xfer' which sends a request, creates a Linux
completion, and calls 'wait_for_completion_timeout'. This leads to a
blocking of the task and a call to the task scheduler. Since there
should be nothing to schedule at this point, the entrypoint will
eventually return to its "wait for RPC" code. When the waited for IRQ
occurs, the entrypoint receives a signal RPC and wakes up yet another
task, the IRQ task
(dde_linux/src/lx_kit/irq.cc:Lx_kit::Irq::Context::unblock). This task
calls all registered interrupt handlers ('handle_irq' same file). One of
those handlers should, behind your back, call 'complete' (I haven't
found the relevant source code for your case, but it is there) for the
completion your task is waiting for, which in turn should unblock your
task. This way a synchronous execution is accomplished. That is the theory.

Details:

'wait_for_completion_timeout'
(dde_linux/src/include/lx_emul/impl/completion.h) will call
'__wait_completion' which must be implemented by your driver. Please
refer to '__wait_completion' (dde_linux/src/lib/usb/lx_emul.cc) as a
guidance. The important part is to call 'block_and_schedule' for the
current task. Also notice, the 'complete' function in completion.h that
calls 'unblock' for the task within a completion. This should somehow be
called by your interrupt handler and lead to the re-scheduling of your
task when the IRQ tasks blocks again after interrupt handling.

By the way, these Lx::Taks are also called routine or coroutine in
literature and nothing more than a stack and a 'setjmp/longjmp' construct.

I hope this helps,

Sebastian


-- 
Sebastian Sumpf
Genode Labs

http://www.genode-labs.com · http://genode.org

Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth